1. Field of the Invention
The present invention relates to a light source apparatus for an endoscope which can control an amount of outgoing light from a light source portion in a lighted state and a control method for the light source apparatus for the endoscope.
2. Description of the Related Art
A light source apparatus which supplies light to be applied from a distal end portion of an endoscope (scope) to a subject is provided with a light source portion (hereinafter referred to as a lamp) which generates light. Such a lamp decreases in the amount of emitted light or light emission luminance becomes more unstable as a used time period becomes longer, which creates a need for replacement. Under the circumstances, a technique is proposed for prolonging a life of a lamp as much as possible.
For example, Japanese Patent Application Laid-Open Publication No. 2003-131324 describes a discharge lamp lighting apparatus of a projection type image apparatus which has a plurality of power modes available and shifts to a power mode with lower power consumption according to a continuous lighting time period of the lamp, which is different in field from an endoscope. The continuous lighting time period here refers to a total used time period from when a new lamp starts to be used. A power value in each power mode is a value of power actually supplied to a lamp.
Japanese Patent Application Laid-Open Publication No. 2011-124109 describes an illuminance sensorless illumination control system that gauges a cumulative lighting time period with a timer and, when the cumulative lighting time period reaches a predetermined time period, controls a light adjustment output value to a light adjustment output value determined in consideration of a maintenance factor, which is also different in field from an endoscope. The cumulative lighting time period here refers to a total used time period from when a new light source starts to be used. Note that the technique described in Japanese Patent Application Laid-Open Publication No. 2011-124109 is not intended to prolong a lamp life and is configured to perform control that increases a light adjustment output value in order to compensate for decrease in illuminance due to use-induced degradation (see, e.g., paragraph [0041] and FIGS. 2 to 4 of the publication).
Japanese Patent Application Laid-Open Publication No. 2004-31283 describes a technique for obtaining a cumulative energization time period of a light source and reducing, in a stepwise manner, a driving current for the light source with increase in the cumulative energization time period, which is targeted for a liquid crystal display apparatus or the like and is different in field from an endoscope. The cumulative energization time period here refers to a total used time period from when a new light source starts to be used. The current reduced with the cumulative energization time period is a driving current which is actually supplied to the light source. The publication also describes a technique for increasing or reducing the driving current for the light source according to whether surroundings of the light source are bright or dark. More specifically, the technique switches between a D mode corresponding to daytime and an N mode corresponding to nighttime.
The technique described in each publication described above is a technique for controlling power supplied to a light source according to a total used time period from when a new light source starts to be used.